Impedance devices, such as impedance wires and catheters, have dimensional requirements that require such devices to not only be small enough to advance through mammalian luminal organs of various sizes, but also small enough to be used in connection with other devices (such as guide catheters). The size requirements (such as overall device diameter) generally constrain a developer of such a device when certain device functionality is desired.
Over several decades medical diagnostic and therapeutic interventional procedures have become less invasive due in part to the use of more percutaneous surgical approaches, which access the intravascular system and organs through the skin with a needle. Typically the first medical device through these needles is a guidewire. The guidewire is navigated to the location of interest by use of fluoroscopic imaging, MRI, or other imaging modalities. The guidewire, once navigated to the site of interest, becomes the access pathway for a variety of catheters needed to complete the percutaneous interventional procedure.
There exists a significant need to reduce the total cost of care for these percutaneous procedures and the diseases they are treating. Recent solutions to this need include, among other things, an increase in smart devices to quickly, accurately and intelligently diagnose and inform the interventional procedure. This solution includes adding sensors to guidewires. A clinical application such as angioplasty/stenting to open a vessel stenosis may ideally use intravascular pressure sensing to determine pressure changes in a vessel of interest and the applicability of therapy. Once a pressure gradient or fraction flow reserve is determined to be significant, a clinician may want to use intravascular sensors to more accurately size the vessel, determine location of lipid pools, determine thickness of lipid pool caps, determine force being applied to tissues, or even assess post therapy information. Ideally all of this sensor information will be derived from the guidewire as the common tool which initially accesses and remains across the site of interest.
Another solution to this reduced cost clinical need is the creation of smaller interventional devices. This includes devices for radial access, reducing hospital stays. It also includes treating problems earlier in more vascular distal locations. The need for smaller percutaneous devices includes guidewires. This is not easily done however; because often the entire guidewire cross section needs to consist of a high modulus material such as stainless steel in order to provide sufficient support for diagnostic and/or therapy delivery catheters. Coronary guidewires for instance are 0.014″ in diameter and most of the guidewire length is constructed of a core which is close to 0.014″ in diameter, and often these are not stiff enough in lateral bending. Also, this same maximizing of Young's modulus and diameter translates into improved torque and steerability performance, which is critically important in guidewires since it is this device that the clinician uses to guide access to the site of interest.
Adding the needed sensor conductors over the length of the guidewire can take cross-sectional area and thus reduce the lateral stiffness, torsional stiffness and torsional control of the guidewire, and therefore increase guidewire delivery time, catheter delivery time, device cost and possibly total cost of care. An example of this is the marketed pressure sensing guidewire made of hypo tubes. The hypo tube is used instead of a guidewire core with a full cross section of metal so sensor conductor wires can be run down the inside of the hypo tube core, from the proximal end of the guidewire to the distal tip of the guidewire enabling the pressure sensor. Unfortunately the use of a hypo tube for the guidewire core gives this device undesirable lateral stiffness and clinical device delivery characteristics.
Furthermore, currently contemplated guidewires using pressure sensors are generally limited to enabling the dual combination of the necessary mechanical characteristics and pressure sensing. But vessel sizing, imaging, temperature, or other sensing modalities, which may further minimize procedure cost and improve therapeutic outcomes, are not enabled, either alone or in combination.
There remains a need for a higher performance guidewire that is capable of quickly and accurately measuring multiple biological metrics while maximizing high performance mechanical characteristics. In view of the same, impedance devices, and systems incorporating the same, having desired functionality with fewer parts than would normally be required and/or having components/componentry small enough to permit desired device operation, would be well received in the marketplace and solve a number of problems facing impedance device developers.